Question

The products of respiration is
a. Water
b. Carbon dioxide
c. Energy
d. All of the above

Answer 1

Hint: Respiration is an exergonic and catabolic-physio-chemical process that involves the exchange of environmental oxygen and body carbon dioxide through a liquid medium and the oxidation of glucose inside the mitochondria to produce energy, stored in the high energy bonds of ATP molecules.

Complete answer:
Cell respiration is an enzymatically controlled chemical process in which the glucose is oxidized inside the mitochondria to release energy.
 It is a stepwise reaction which means that energy is not released free into the cell or in a single step. It is released in a series of stepwise reactions controlled by enzymes to trap the chemical energy in the form of ATP i.e, adenosine triphosphate.

It is of two types:
- Aerobic respiration occurs in mitochondria in presence of oxygen. The end products of this respiration are carbon dioxide, water and energy.
- Anaerobic respiration or fermentation involves the production of energy from the food nutrients in the absence of oxygen.

It involves glycolysis in which one molecule of glucose is degraded into two molecules of pyruvic acid, two ATP molecules and two NADPH2 molecules. Pyruvic acid acts as an H-acceptor. Depending upon the metabolic pathways the end-product of anaerobic respiration is either ethanol and carbon dioxide as in yeasts or lactic acid as in some bacteria and muscles in the human body.

Hence, the correct answer is option (D).

Note: The compounds that are oxidized during respiration are called respiratory substrates. Mainly carbohydrates are used by organisms as respiratory substrates to get energy but under some conditions in some organisms fats, proteins and organic acids are also used as respiratory substrates.